1. Field of the Invention
The invention relates to a SRAM cell apparatus, particularly to a dual-threshold-voltage two-port sub-threshold SRAM cell apparatus.
2. Description of the Prior Art
The Static Random Access Memory (SRAM) is a kind of Random Access Memory (RAM). It means if the electric power is kept in the SRAM, the data will be able to be stored in it constantly. On the contrary, the data stored in the Dynamic Random Access Memory (DRAM) has to be upgraded periodically, and when the power supply is cut off, the stored data will be disappeared, which is completely different from the Read-Only Memory (ROM) or flash memory.
Thus, in the semiconductor memory devices, compared with the above-mentioned DRAM, the SRAM can provide the advantage of lower power consumption, and faster operation speed. Therefore, the SRAM can be widely used as the flash memory in the computer or in the other portable devices.
In the prior art, generally the SRAM often contains a wordline driver for receiving a word selection signal from an encoder. The wordline driver usually contains the inverters which are composed of the elements with smaller channel length and wider width. These inverters are used to adjust the voltage level on the wordline upon write program and read data. The inverter usually contains a pair of P-type Metal Oxide Semiconductor (PMOS) transistor and N-type Metal Oxide Semiconductor (NMOS) transistor. These two transistors are connected by a complementary power supply in serial, in order to generate a reverse signal corresponding to an input signal. The above-mentioned SRAM is widely applied in various single chip systems at present.
Although single chip systems can be used in many specific fields, such as the biomedical and electronic fields etc., but the single chip system stress has to have the characteristics of high reliability, low-voltage operation, low power consumption, and good stability etc. Thus, the design of SRAM is still unable to meet the above-mentioned requirements in the industry at present.
Therefore, in order to respond the technology demand for the production of SRAM, it is necessary to develop relevant process and technology to reduce the cost of operation manpower and manufacturing time, and reach the goal of energy conservation and carbon reduction effectively.